Rotary contact



J1me 1965 J. A. MASTERS ETAL' 3,

ROTARY CONTACT Filed Feb. 1. 1962 INVENTORS JOHN A. MASTERS y WILLIAM M COOPER ATTORNEY United States Patent 3,189,861 ROTARY CONTACT John A. Masters and Wiliiam M. Cooper, Liverrnore, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 1, 1962, Ser. No. 170,527 6 Claims. (Cl. 339-8) The present invention relates to electrical contacts and, more particularly, to rotary contacts, wherein contact is maintained through the use of liquid conductors. In general, the invention comprises a terminal-to-terminal contact maintained by mercury-filled channels. Channel housings rotate a set of terminals with respect to another set of terminals, while maintaining virtually noiseless electrical contact between corresponding terminals of each set.

In the prior art, rotary contacts, for the most part, have been characterized by the use of terminals which are disposed in rotatable, mechanical, and electrical connection with one member sliding over another. However, numerous characteristics of rotary contacts, as known in the art, are objectionable in certain applications. Where sensitive electronic equipment is being used, the electrical noise generated by metal sliding over metal is often above the allowable maximum, even where the most refined contacts are used. Other deficiencies common to such contacts is the tendency to Wear, to change relative position, to corrode, to oxidize, to pit, etc. In addition, their useful lifetimes are limited by arcing from one member of the contact to the other.

The present invention provides a virtually noiseless rotary contact, which is unaffected by the atmosphere, maintains a path of electrical communication even though a first set of terminals is rotated relative to a second set, and has a lifetime far in excess of normal requirements. A non-conducting housing with concentric cylindrical channels containing a conducting fluid, provides the means by which noiseless operation is achieved.

It is therefore an important object of the present invention to provide a rotary contact which does not generate detectable electrical noise.

A further object of the invention is to provide a rotary contact which is virtually corrosion-free, therefore possessing a useful lifetime in excess of that common to the art.

Yet another object of the present invention is to provide a rotary contact with little or no attenuation or distortion.

Other objects and advantages of the invention will become apparent by consideration of the following description taken in conjunction with the accompanying drawing, of which the single figure is an isometric, sectional view of the rotary contact of the invention.

Considering now the invention as to its general aspects, the rotary contact comprises a two-part, non-conductive housing with mating concentric channels formed therein. The channels, in turn, contain mercury or other suitable conducting liquids. The use of nylon as the housing material has been found to be superior to other non-conductors due, in part, to the low coefficient of friction exhibited when one piece is rotated with respect to another, even though they are pressed tightly together. Nylon is also mechanically stronger than many other non-conductors, easier to fabricate, and less expensive.

The use of mercury has been found to be superior to other conducting fluids, such as, saline solutions of water, partially as a consequence of its low tendency to evaporate and to oxidize the terminals.

In the figure, there is shown a rotary contact 11 providing electrical continuity between terminals 12, 12 and terminals 13, 13' respectively, while enabling either set of terminals to rotate with respect to the other.

Terminals 12, 12 are retained in a cylindrical housing 14 of a nylon plastic, or its equivalent. A pair of cylindrical channels 16, 16 are formed in housing 14 so as to be concentric to each other and coaxial within the housing. The channels 16, 16 are open at the base 17 of housing 14, while terminals 12, 12 enter channels 16, 16, respectively, through base portion 20 of housing 14.

A second cylindrical housing 18 is shown, similar to housing 14, which coacts and engages therewith by means of a tongue and groove mating portion 19. Housing 18 has a pair of concentric channels 21, 21, which communicate with channels 16, 16', respectively, when housings 14 and 18 are connected. Terminals 13, 13 communicate with channels 21, 21', respectively, in the same manner as terminals 12, 12, communicate with channels 16, 16'. A spring-loaded bolt 22 and nut 23 act through bearings 27, 2-7, seated adjacent to washers 26, 26', on hearing races 28, 28', and through a central bore 24 to rotatably secure housings 14 and 18 together. More specifically, coil spring 29 is disposed between flange 30 on the shank of bolt 22 and washer 26, to spring load said bolt 22 and nut 23.

When the two housings are securely contacted, channels 16 and 21, and 16' and 21', combine to form closed concentric cylinders. These cylinders are filled with mercury through a terminal hole so as to provide a conductive path between terminal 12 and 13, and 12' and 13. The tongue and groove joint between the housings prevents mercury leakage and provides good rotational surfaces which operate for extended time without noticeable wear.

It is seen that electrical contact between terminals 12 and 13, and 12' and 13, is maintained (through the mercury-filled cylinders), no matter if terminals 12, 12 are rotated relative to terminals 13, 13'. The absence of solid metal sliding on solid metal enables rotary contact to be maintained with undetectable noise generation and essentially zero distortion or attenuation. In one actual connector constructed, the resistance between non-corresponding terminals was found to be between 100,000 megohms and infinity.

Numerous modifications to the invention are possible. These include the use of a metallic, circular conductor affixed within the closed base of channels 16, 16, 21, 21', and in contact with their respective terminal posts. This maintains electrical continuity (even when the mercury level is reduced), as long as some parts of the conductor are in contact with the mercury.

The rotary contact 11 is also convertible to a rotary switch by making the channels less than complete cylinders.

One of many uses for the present invention is as follows: Terminals 12, 12', are connected to a portable piece of electrical equipment. Terminals 13, 13 are connected to the interior end of a drum-wound cable. The other end of the cable is then connected to a stationary power supply. The drum can then be rolled along with the portable equipment without either breaking the electrical contact or kinking the cable.

It is to be understood that the form of the present invention, herewith shown and described, is to be taken as a preferred example of the same and that various changes in the shape, size, material, constitution, and arrangement of parts may be resorted to without departing from the spirit of said invention or the scope of the subjoined claims.

What is claimed is:

1. In a low-noise electrical rotary contact, the combination comprising,

(a) a first generally solid, right-cylindrical non-conducing member having a plurality of concentric annular channels formed into one of the planar surfaces thereof, said member also defining an axial bore extending along the axis of rotation thereof,

(b) a second generallysolid, right-cylindrical non-conducting member having a plurality of concentric annular channels formed into one of the planar surfaces thereof, said member also defining an axial bore extending along the axis of rotation thereof, the channeled surface of said second cylindrical member being disposed in adjoining rotatable contact with the channeled surface of said first cylindrical member with respective annular channels registering to form closed annular conduits,

(c) mating tongue and groove means formed into the adjoining planar surfaces of said first and second cylindrical members concentrically to said annular channels,

(d) spring-loaded means including a bolt extending through said axial bores of said members, annular bearing races on the non-adjoining surfaces of said cylindrical members concentric to said bores, bearings positioned within said races, keeper means disposed about said bolt adjacent said bearings for maintaining saidbearings in said races, and spring means disposed about said bolt, said bearings, keeper means, and spring means cooperating with said cylindrical members to maintain the registry of said channels,

(e) an electrically conductive fluid disposed Within and filling said closed annular conduits, and

(f) a plurality of electrical terminals extending through each of said cylindrical members and contacting said fluid, said fluid being the only means of electrical communication between the terminals extending through the first cylindrical member and those terminals extending through the second cylindrical member.

2. A low-noise electrical rotary contact as recited in claim 1 wherein,

(a) said first and second cylindrical members consist of nylon,

(b) said electrically conductive fluid consists of mercury metal, and

(c) said electrical terminals are straight-Wire pins and disposed parallel to the common axis of rotation of said non-conducting members.

3. In a low-noise electrical rotary contact, the combination comprising:

centrically with respect to said axis of rotation, the channeled surface of said second member being disposed in adjoining rotatable contact with the channeled surface of said first member with respective annular channels registering to form closed annular conduits and with said axial bores in mutual alignment;

(c) mating tongue and groove means formed into adjoining planar surfaces of said first and second members concentrically to said annular channels;

(d) spring loaded mean-s including a bolt extending through the axial bores of said non-conducting member, the diameterof said bolt being substantially less than that of said axial bores, annular bearing races disposed on the non-adjoining surfaces of said members concentric to said bores, bearings positioned Within said races, keeper means disposed about said bolt adjacent said bearings for maintaining said bearings in said races, and spring means disposed about said bolt, said bearings, keeper means, and spring means cooperating with said members to maintain the registry of saidchannels; V

(e) an electrically conductive fluid disposed within and filling said closed annular conduits; and

(f) a plurality of electrical terminals extending into each of said non-conducting members, and contacting said fluid, said fluid being the only means of electrical communication between the terminals extending through the first non-conducting member and those terminals extending through the second nonconducting member.

4. A low-noise electrical rotary contact as recited in claim 3 wherein said first and second non-conducting members consist of nylon.

5. A low-noise electrical rotary contact as recited in claim 3 wherein said electrically conductive fluid consists of mercury metal.

6. A low-noise electrical rotary contact as recited in claim 3 wherein the electrical terminals are'straight-wire pins and disposed parallel to the common axis of rotation of said first and second non-conducting members.

References Cited by the Examiner UNITED STATES PATENTS 995,100 6/11 Siegenbruch 339-108 1,241,030 9/17v Schade 339-8 1,404,097 1/22 Dennis 339-8 1,667,660 4/28 Gehm 339-8 1,934,799 11/33 Gunby 339-8 2,134,355 10/38 Caldwell 339-8 2,832,056 4/58 Stutzman 339-5 2,890,304 6/59 Cole 200- 3,014,192 12/61 Leslie 339-5 OTHER REFERENCES Du Pont: Plastics Bulletin No. 47 (1950), page 188.

JOSEPH D. SEERS, Primary Examiner. ALFRED s. TRASK, Examiner. 

1. IN A LOW-NOISE ELECTRICAL ROTARY CONTACT, THE COMBINATION COMPRISING, (A) A FIRST GENERALLY SOLID, RIGHT-CYLINDRICAL NON-CONDUCING MEMBER HAVING A PLURALITY OF CONCENTRIC ANNULAR CHANNELS FORMED INTO ONE OF THE PLANAR SURFACES THEREOF, SAID MEMBER ALSO DEFINING AN AXIAL BORE EXTENDING ALONG THE AXIS OF ROTATION THEREOF, (B) A SECOND GENERALLY SOLID, RIGHT-CYLINDRICAL NON-CON DUCTING MEMBER HAVING A PLURALITY OF CONCENTRIC ANNULAR CHANNELS FORMED INTO ONE OF THE PLANAR SURFACES THEREOF, SAID MEMBER ALSO DEFINING AN AXIAL BORE EXTENDING ALONG THE AXIS OF ROTATION THEREOF, THE CHANNELED SURFACE OF SAID SECOND CYLINDRICAL MEMBER BEING DISPOSED IN ADJOINING ROTATABLE CONTACT WITH THE CHANNELED SURFACE OF SAID FIRST CYLINDRICAL MEMBER WITH RESPECTIVE ANNULAR CHANNELS REGISTERING TO FORM CLOSED ANNULAR CONDUITS, (C) MATING TONGUE AND GROOVE MEANS FORMED INTO THE ADJOINING PLANAR SURFACES OF SAID FIRST AND SECOND CYLINDRICAL MEMBERS CONCENTRICALLY TO SAID ANNULAR CHANNELS, (D) SPRING-LOADED MEANS INCLUDING A BOLT EXTENDING THROUGH SAID AXIAL BORES OF SAID MEMBERS, ANNULAR BEARING RACES ON THE NON-ADJOINING SURFACES OF SAID CYLINDRICAL MEMBERS CONCENTRIC TO SAID BORES, BEARINGS POSITIONED WITHIN SAID RACES, KEEPER MEANS DISPOSED ABOUT SAID BOLT ADJACENT SAID BEARINGS FOR MAINTAINING SAID BEARINGS IN SAID RACES, AND SPRING MEANS DISPOSED ABOUT SAID BOLT, SAID BEARINGS, KEEPER MEANS, AND SPRING MEANS COOPERATING WITH SAID CYLINDRICAL MEMBERS TO MAINTAIN THE REGISTRY OF SAID CHANNELS, (E) AN ELECTRICALLY CONDUCTIVE FLUID DISPOSED WITHIN AND FILLING SAID CLOSED ANNULAR CONDUITS, AND (F) A PLURALITY OF ELECTRICAL TERMINALS EXTENDING THROUGH EACH OF SAID CYLINDRICAL MEMBERS AND CONTACTING SAID FLUID, SAID FLUID BEING THE ONLY MEANS OF ELECTRICAL COMMUNICATION BETWEEN THE TERMINALS EXTENDING THROUGH THE FIRST CYLINDRICAL MEMBER AND THOSE TERMINALS EXTENDING THROUGH THE SECOND CYLINDRICAL MEMBER. 